The interview process has the following steps:

1. Initial recruiter interview
2. Assignment
3. Technical interview
4. Team interview
5. Final Interview

The assignment was an interesting one with lots of restrictions/conditions. That itself was a warning sign regarding the engineering culture. Nevertheless, because of the excitement in the problem, I proceeded to do it. The feedback I received was that even though the concurrency requirements were met, the solution had two cons:

• Lack of a service layer, which I mentioned in the README explicitly, done only because it's an assignment (which, afaik, is to check your coding style!).
• Throwing exceptions in the controller. This is perfectly fine as there was ControllerAdvice functionality built in to deal with the error response (with default spring boot settings).

It was unfathomable to think the way the reviewer judged the applicant, saying the applicant doesn't know about basic layering in coding practice, even though the code was structured with immutability, concurrency, and domain-driven design practices.

So, basically, they are running it against a checklist, or some mid-senior people are in charge of the process who have some rigid views on software development practices. Basically, you have to stick very much to the template way of doing development, and there is no room for doing it as a fun assignment anyway, otherwise you won't even get an opportunity to explain your assignment.

The assignment is to build a highly concurrent API service.